SEQUESTRATION OF DIETARY SECONDARY METABOLITES BY 3 SPECIES OF SEA HARES - LOCATION, SPECIFICITY AND DYNAMICS

We examined the location of sequestered secondary metabolites in three species of sea hares, Stylocheilus longicauda, Dolabella auricularia, and Aplysia californica (Opisthobranchia: Anaspidea). The sea hares a te a natural diet or were fed an artificial diet containing secondary metabolites in the laboratory. In all three species, sequestered secon dary metabolites were located almost exclusively in the digestive glan d, an internal organ, rather than in the exterior parts of the body, i n eggs, or in ink (released when sea hares are disturbed). S. longicau da, a specialist sea hare, was able to sequester measurable amounts of all six algal metabolites offered (caulerpenyne, halimedatetraacetate , pachydictyol A, malyngamides A and B, and ochtodene) and two (luffar iellolide and Dysidea spp. brominated diphenyl ether) of three sponge metabolites offered (chondrillin was not sequestered). Malyngamides A and B, found in the host plant of S. longicauda, were sequestered at h igh, but not unique concentrations. D. auricularia, a generalist sea h are, was fed caulerpenyne, pachydictyol A and malyngamide B; patterns of sequestration of these three compounds did not differ markedly betw een S. longicauda and D. auricularia. S. longicauda did not lose measu rable amounts of malyngamides after 18 d on a malyngamide-free diet. T hese results suggest that sea hares have generic mechanisms for seques tering algal metabolites rather than mechanisms that are tightly linke d to particular compounds, that these mechanisms do not differ dramati cally between species, and that sequestered secondary metabolites are not located optimally for defense.